10 



PROCESSING OCEANOGRAPHIC DATA 



increases -with depth, indicating that the wire 

 becomes more vertical vdth depth. 



If the ratio plot is not a reasonably smooth 

 curve the data should be studied for errors. 

 Occasionally bottles reverse prematurely, thci-- 

 mometers stick, meter wheels operate improp- 

 erly, readings are made incorrectly, and other 

 instrumental and human errors occur. Han- 

 dling these types of data requires considerable 

 experience, knowledge of individual pieces of 

 equipment, and familiarity with the area to 

 detect, and in some cases correct, errors in 

 the data. If, for any reason, the equipment 

 fails to give correct thermometric depths the 

 results must not be used. In figure 12, for ex- 

 ample, the calculated depth for the 1,000-metcr 

 wire depth appears to be in error and must be 

 discarded. 



A modification of the above method (Reid, 

 1949, and Pollak, 1950) (10) of calculating 

 interpolated depths from the thermometric 

 depths is by plotting the difference between 

 wire length and the thermometric depth against 

 wire length, as shown in figure 13. 



The smooth curve drawn will be tangent at 

 the surface to a line determined by wire angle 

 from the ship. This line will show a difl'erence 

 between the wire length and the depth of 

 "1 — cosine wire angle" per unit of wire length. 

 A quarter sunburst of lines for different wire 

 angles radiating from the surface maj be printed 

 on the graph in advance, eliminating calcula- 

 tion. From the smooth curve, values of wire 

 length minus depth arc read corresponding to 

 the wire length to each water bottle. By sub- 

 tracting each of these values from wire length 

 the accepted depth of each water bottle is 

 found. This curve, like the former ones to 

 obtain interpolated depths, must be studied for 

 errors. From the nature of this graph certain 

 errors are apparent; for example, no value of 

 wire length minus depth can be negative, nor 

 can the curve have a negative slope, since this 

 would indicate stretching of wire. Other theo- 

 retical criteria are that the curvature normally 

 increases with depth and the wire angle becomes 

 practically zero at the end. Since the curve is 

 roughly similar to the actual shape of the wire 

 in the water, inflection points may, however, 

 indicate depths of current gradients. An ex- 



Figure 13. — Graph for determining depths of observation 

 between calculated thermometric depths by the difference 

 method (wire length minus thermometric depth). 



ample of the calculation of accepted depths by 

 this method is given in figure 14. 



VALUES AT STANDARD DEPTHS 



When the accepted depths have been estab- 

 lished the next step in the processing of serial 

 observations is to prepare plots of the vertical 

 distribution of the variables. All variables may 

 be plotted by station, as in figure 15, or by 

 property. Such plots of temperature, salinity, 

 etc., as a function of depth are useful to detect 

 incorrect values resulting from faulty operation 

 of thermometers and water bottles. Another 



